Project Summary Communities that practice traditional land-based cultures are intimately connected to the environment due to cultural, spiritual, and traditional practices. While our Center?s previous work demonstrated varying degrees of metal exposure among members of Navajo Nation, Cheyenne River Sioux (CRST) and Apsalooke (Crow), single exposure pathway (e.g. water) investigations were not sufficient to explain individual-level exposure and adverse health outcomes. Moreover, there remains limited knowledge on other chemical exposure sources prominent on Tribal lands, such as trash burning, that may lead to accumulation of microplastics, volatile, and semi-volatile compounds in the environment and lead human exposures. This research project will address the challenge of integrating multiple exposure routes for Native communities through modeling combined environmental exposure potential. We will adapt an existing GIS-based multi-criteria decision analysis approach that can integrate air, water, and soil pathways previously used by our group. Our modeling framework enables integration of novel soil, water, air, and plant data on microplastics and other chemicals produced by low-temperature trashing combustion. This research approach is innovative because it investigates combined exposures on tribal lands, including microplastics and combusted plastic by-products against a background of high metal exposures. We will (1) develop predictive and validate combined environmental exposure models based on GIS-based multi-criteria decision analysis, which considers chemical sources, topography, infrastructure, and land-use practices; (2) ground truth model predictions through measurement of combined exposures for people and cultural resources (such as livestock and plants) using silicone wristbands, human biomonitoring, and immunology studies; and (3) collect community-scale health survey data to begin assessing exposure :disease relationships (e.g., cancer, autoimmunity, and cardiovascular disease) in collaboration with RP3. SA1 will generate the first combined environmental exposure spatial products for Apsalooke (Crow) and Crow and CRST reservation lands and a refined product for NN. These spatial products will support environmental health research among Tribal communities and provide policy-makers with critical information to address Tribal health disparities. The studies proposed in SA2 provide important ground truthing of the GIS-based model through individual-level chemical and immune marker measurements. This will inform policy makers about the scope and extent of combined environmental exposures in their communities and allow us to consider the contributions of combined chemical exposures to associations with metals that we have observed in participant samples from these communities. The health survey data will provide data to validate and substantiate health disparities at individual community scale for tribal community partners, and at a scale consistent with the combined exposure prediction scale in our model.